Cathode ray device



July 14, 1931. w. J. HITCHCOCK CATHODE RAY DEVICE Filed Nov. 26. 1929 Inventor: William d. HitchcocK,

H is Attorney.'

Patented July 14, 1931 UNITEDy STATES PATENT OFFICE WILLIAM J. HITCHCOCK, OF SCOTIA, NEW YORK, ASSIGNOR TO GENERAL ELCTRIC COMPANY, A CORPORATION OF NEW YORK cATHoDE RAY DEVICE Application filed November 26, 1929. Serial No. 409,957.

My invention relates to the transmission of pictures or images particularly to cathode ray devices employed therein and has for its principal object the provision of an improved apparatus and method of operation whereby the light-s and shadows of the picture are simultaneously converted into corresponding voltages which are successively transmitted without dangerv of short circuit through the capacity coupling between the various parts and connections of the apparatus.

In the past various types of cathode ray photo-electric cells have been provided Jfor producing electrical impulses which are dependent on the shade of the successive elemental areas of a picture. In the operation of' such devices it is vfound that they have enough ca acity between the anode and ground to s ort circuit to a large extent any considerable resistance placed in series with them. The result is thatthe power which can be derived from such devices, especially at high frequencies, is limited. 1It is therefore desirable that the photoelectric device be so constructed that its anode circuit possesses a high im edance, thus permitting a larger amount o power to be derived from it than has heretofore been ossible. Such devices as hereto ore constructed usually include a cathode, an auxiliary anode for accelerating the cathode ray, a grid, a hotoelectric surface and an anode. It has een proposed to connect the photoelectric surface to some point in the anode circuit of the device and' to divide this surface into a plurality `of small sections each of which are subjected to a Voltage corresponding to one elemental area of the picture.

In order that the capacity of the device be V as small as possible, 1t is desirable that no metallic connection be provided between the small elements of the photoelectric surface and the other parts of the device. The capacity between each element of the photoelectric surface and its surroundings depends on its size and its spacing from neighboring elements and other objects. The resistance between each element and the ground is` dependent on conduction throu h the element supports, leakage over the sur ace of the supports and the resistance of whatever is effected by the electric charge on the surface.

Conduction to ground is a mattei' of the specific resistance of the material on which the photoelectric surface is deposited, and while it cannot be altogether eliminated, it

lcan be minimized to any desired degree by :making the surface support sufficiently thin.

If the photo-electric surface is caesium leakage over the surface support is not objectionable as the caesium is referably in the form of a very thin layer. "xperience shows that the coating may be vso thin that there is substantially no leakage on the surface of the glass support. In accordance with my invention such a material as silver, copper, acquadag or the like is deposited on a vitreous support such as glass cloth consisting of thin threads so spaced and of such size that they will have little capacity to their surroundings and will be well insulated from each other.

The size of each separate element of the surface is not determined by light considerations since an image can be as small as desired without affecting the quantity of light. In order for the capacity to be suiiciently small, however, the surface must be small, yet still large 'enou h to affect whatever it is proposed to control gy the charge on the photo-electric surface.

In order to successively transmit the voltages simultaneously produced on the different elements of the photo-electriesurfaces, it is desirable to utilize a cathode ray which is caused to scan the photo-electric surface. The usev of the cathode ray in this manner would seem to involve conflicting requirements because the ray must be narrow if it is to be sufficiently controlled by a point object Ain its path. In practice the narrownessof the ray, particularly for small anode voltages, is secured by introducing gas into the device with the result that positive ions are generated in the path of the electrons and hold them in a pencil which can be made to have a diameter of less than l millimeter.

If the various parts of the apparatus are so arranged thatthe electrons transmitted between the main cathode and anode do not reach but pass between/the photo-electric surfaces, lwhich is a necessary condition for the photo-electric surface to functlon substantially as a purely electrostatic device with high resistance to ground, the negative poindiscriminately distributed over the photoelectric surface, thus causing it to tend to assume substantially the same potential as the auxiliary cathode. It is desirable that this I sistance to ground as it is controllable to meetY sort of resistance to ground be the onlyrethe condition that the time constant of the condenser formed by each element of the photoelectric surface and its surroundings'r` should be of the order of 1/16 of a second. Under these conditions the photoelectric surface is not discharged appreciably during the time that it is subjected to the cathode ray if positive ions are prevented from reachinc it.

rn order to prevent the positive ions from reaching the photoelectric surface, a suitable collector for them and a grid are so mounted with respect to the photoelectric surface that the ray projected from the cathode is slowed down until no positive ions are generated in the space between the grid and the photoelectric surface.

My invention will `be better understood from the following description when considered in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 illustrates the construction and circuit arrangement of an apparatus involvingmy invention; and Fig. 2 illustrates a detailed construction of the photo-electric cathode ray device of Fig. l.

The apparatus illustrated by Fig. 1 includes a photo-electric cathode ray device 10, which is provided with a main cathode 11, an auxiliary cathode 12, electrostatic control electrodes 13 and `14, control electrodes 15 and 16, a photo-electric surface 17 and an anode 18. The cathodes 11 and 12 are connected in series with a resistor 19 through a lbattery 20, the cathode 12 being maintained at a potential which is more negative than that of the cathode 11. The cathode 11 is associated with a screen 21 and an accelerating anode 22; The cathode 12 is associated wit an accelerating anode 23 and is so arranged that the electrons emitted by it are not con- As previously indicated, it is undesirable that positive ions be produced' in the vicinity of the photoelectric surface 17. The potential .of the photoelectric surface becomes more positive as the intensity of the light to which it is subjected increases. In order to decelerf ate the electrons so that the photoelectric surface will not be affected by positive ions, the control members15 and 16 are provided. It will be observed that the control electrode 16 is connected to the cathodes 11 and 12 through a potential 'source 24 and that the control electrode 15 is connected to the cathodes through a potential source 25 and the source 24 whereby this electrode is subjected to la 'potential which isv more negative than that of the electrode 16. The potentials applied to the control electrodes 15 Aand 16 should be such that the space etween the electrode 15 and the photoelectric surface 17 and so that the potential of each photoelectric surface shall be a considerable fractionof all potentials acting on the Aelectrons in the space between the electrode 15 and the photoelectric surfaces 17. Under these conditions the charges on the photoelectric surfaces act in the same manner as an electrostatic grid to. control the electrons in their motion toward the anode 18. The electrostatic design of grids for such purposes is well known and needs no discussion.

The anode eircuit'of the device 10 includes a resistance 26, a battery 27 and the batteries 24 and 25. This circuit is connected in a well known manner to the input circuit of a radio transmitter 28 though a condenser 29.

A preferred construction of the control electrodes 15 and 16, the photoelectric surface 17 and anode 18 is illustrated by Fig. 2. As indicated, the electrodes 15 and 16 and the anode 18 may be formed of a plurality of conductors arranged transversely of one another. The photoelectric surface 17 preferably consists of a photoelectric material mounted upon a plurality of conducting surfaces deposited as small-spots on vitreoussupports such as glass cloth.

ln the operation ofy the apparatus, light .from a picture or image 30 is projected through a lens 31 and the 'anode 18 on the photoelectric surface 17. By means of this light, voltages 'corresponding to the shade ositive ions are not generated in.

surfaces being determined by the electric I charge produced on itvby the light Whichit receives from the image 30, Under these conditions, electrical impluses corresponding to the light .applied to each element of the photoelectric surface are successively applied to the input circuit of themadio transmitter 28 through which tley are transmittedto any suitable receiving apparatus. Due

to the fact that the described construction of the device results in an anode circuit of much higher impedance than that heretofore realized in the operation of such devices, the power output applied to the input i circuit of the radio transmitter is `ymuch greater than has heretofore been realized.

f preventing the discharge of a photoelectric control element interpose What I claim as new and desire to secure by Letters Patent of the -United States, is

1. A device including a plurality of cathodes to be maintained at different' potentials, an anode, a photoelectric control element interposed between said anode and cathodes, means for concentrating the ray emitted by one of the said cathodes and means for causing said ray tol scan .said photoelectric element. l 4/ 2'. A device including a plurality of cathodes to be maintained at -different potentials, an anode, a photoelectric control element in terposed between said anode and cathodes, means for concentrating the ray emitted by one of the said cathodes, means for causing said ray to scan said photoelectric element, and means interposed between` said photoelectric element and said'cathodesfor del celerating said ray.

'3. A device including a cathode, an anode, a "photoelectric control' element interposed between said cathode and anode and electrically insulated therefrom, means includ.

ing a gas for concentrating the ray projected from said cathode through said photoelectric element to said anode and means for said element by said ray.

4.y A device including a cathode, an anode between said cathode and anode and electrically `insulated therefrom means including a gas for concentrating the ray rojeetedy from said cathode throu h said` otdelec`I tric element to said an e,7 means for decelerating saidrayin the vicinity of saidl element, and means including an auxiliary cathode for maintaining the-electric charge of said element.

5. An electrode mount for a cathode ray discharge tube comprising a glassv cloth support, a plurality of conductive surfacesmounted on said support, and a coating of photoelectrie material mounted on said support. p

In witness whereof, I have` hereunto set my hand this 25th day of November, 1929. WILLIAM HITCHCOCK. 

